More particularly, the invention relates to a coating intended for road markings, for instance such markings as road center and road verge lines, stop lines, markings which indicate roads that have right-of-way, and pedestrain crossing markings, etc.. The coating can also be used for different types of road signs for instance.
It is a well known problem that although the full beam of a motor vehicle will illuminate satisfactorily the surroundings ahead of the vehicle, it will, at the same time, dazzle the drivers of oncoming vehicles. Although dipped headlights will not dazzle the drivers of oncoming vehicles, the surroundings ahead of the vehicle are not illuminated to a satisfactory extent. The light provided by dipped headlights, however, is normally sufficient to enable the driver of a vehicle to see the road ahead.
However, the ability of a driver to discern road markings and other permanent markings, and also pedestrians, is greatly impaired when driving on dipped headlights, as compared with driving on full beam.
There is a desire, which is becoming more and more pronounced, to equip vehicles with lamps which emit ultraviolet light. Such light causes a number of different pigments to fluoresce to a larger or lesser degree. In recent times, it has become progressively more usual to use so-called daylight pigments or paints, i.e. colours which when excited by ultraviolet light (UV) emit light in the visible wavelength. Light coloured clothing will also fluoresce relatively well when illuminated with ultraviolet light.
In addition to the ability of a vehicle to emit ultraviolet light, it should be possible, with the intention of enhancing safety in traffic, to paint verge posts along the roads, road signs, etc., totally or partially in so-called daylight colours to a greater extent than has hitherto been the case.
It is known to produce road markings which fluoresce when illuminated with ultraviolet light. One such coating is known from U.S. Pat. No. 3,253,146. This coating comprises pigment which fluoresces when illuminated with ultraviolet light admixed with a transparent carrier or matrix.
The known technique in which ultraviolet-fluorescing paints, so-called daylight paints, are used generally requires the use of pigment which will fluoresce when illuminated with ultraviolet light.
One serious drawback with the use of such pigments is that they age relatively quickly.
Swedish Patent Specification No. 8802996-2 (having a corresponding co-pending U.S. application Ser. No. 684,152 with a Swedish priority date of Aug. 26, 1988) teaches a method of producing a so-called road dressing, i.e. a wear layer on roads, said dressing containing mineral which has been doped with dope additives such that the mineral will fluoresce when illuminated with ultraviolet light. This mineral is incorporated in an otherwise dark road surface coating. Despite the large surface area of the road coating, the road surface will fluoresce sufficiently when a vehicle equipped with ultraviolet lamps illuminates the road surface.
One problem with road markings which are intended to fluoresce when illuminated with ultraviolet light is that the markings shall be readily visible when illuminated with natural daylight and when illuminated with artificial light within the visible wavelength range while at the same time producing sufficient fluorescence when illuminated with ultraviolet light, despite the relatively small surface area of the markings. Another problem is one of producing weather durable road markings whose fluorescence properties will remain unimpaired over long periods of time.